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Home >> Ford >> 2002 >> Crown Victoria Base, 4.6 9 >> Repair and Diagnosis >> Restraints >> Air Bag, SRS >> Supplemental Inflatable Restraint System >> Diagnostic Tests >> Test F: Ground Resistance Too High Or RCM Not Mounted To Vehicle Properly (DTC B1921) >> Possible Causes

Possible Causes

Resistance difference between RCM housing ground and terminal ground could be caused by improper tightening of RCM mounting bolts, faulty damaged, terminals or connectors or faulty RCM.

  1. Check for hard or intermittent DTC

    Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). See USING SCAN TOOL  under DIAGNOSTICS. Turn ignition switch to RUN position. Retrieve and record any continuous DTCs. See RETRIEVING FAULT CODES  under DIAGNOSTICS. Perform on-demand self-test. See ON-DEMAND SELF-TEST  under DIAGNOSTICS. If DTC B1921 was retrieved during on-demand self-test, fault is hard. Go to next step. If DTC B1921 was not retrieved, fault is intermittent. Go to step  5 .

  2. Check RCM mounting & bracket

    Turn ignition switch to OFF position. Disable air bag system. See DISABLING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Access RCM. See RESTRAINTS CONTROL MODULE  under REMOVAL & INSTALLATION. Inspect RCM mounting and ensure retaining bolts are fully seated and tightened properly. Remove RCM and visually inspect mounting bracket and mounting surface for damage, corrosion or dirt. If problems are found, repair mounting surface as necessary. Go to next step. If no problems were found. Go to step  6 .

  3. Install RCM & perform on-demand self-test

    Clean mounting surface and bolts. Install RCM. Tighten mounting bolts to specification. See TORQUE SPECIFICATIONS  . Perform on-demand self-test. If DTC B1921 was retrieved during on-demand self-test, go to next step. If DTC B1921 was not retrieved during on-demand self-test, fault is corrected. Go to step  6 .

  4. Check ground circuit for high resistance

    Measure resistance between harness side of RCM connector C310B, terminal No. 10 (Black wire, circuit No. 57) and RCM case. See Figure . If resistance is less than 5 ohms, replace RCM. Go to step  6 . If resistance is more than 5 ohms, repair open in Black wire. Go to step  6 .

  5. Check for intermittent fault

    Turn ignition switch to OFF position. Disable air bag system. See DISABLING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Perform on-demand self-test. If DTC B1921 was retrieved during on-demand self-test, go to step  2 . If DTC B1921 was not retrieved during on-demand self-test, check for cause of intermittent short to ground or open in Black wire (circuit No. 57). See WIRING DIAGRAMS  . Attempt to recreate fault by flexing wire harness and cycling ignition switch frequently. Repair any intermittent problems found. Go to next step.

  6. Check for additional DTCs

    Refer to continuous DTCs recorded in step  1 . If any continuous DTCs were retrieved, go to diagnostic trouble code identification table for direction to appropriate test. See DIAGNOSTIC TROUBLE CODE IDENTIFICATION  table. DO NOT clear any DTCs until all DTCs have been resolved. If no DTCs were retrieved, reconnect air bag system. Activate air bag system. See ACTIVATING SYSTEM  under DISABLING & ACTIVATING AIR BAG SYSTEM. Clear all DTCs. See CLEARING FAULT CODES  under DIAGNOSTICS.
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